Falmouth Group 8

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Station 3

Time: 11:15 (UTC)

Lat: 50 08.963 N

Long: 004 50.039 W

Wind: 350° 13.5 knots

Cloud: 8/8

Click graphs to enlarge

Salinity increases between the surface and 20.5m where it stays constant down to 42.8m. Silicon increases in surface waters slightly from 0.98 μmol/L to 1.00 μmol/L at 20.5m silicon then increases to 2.73 μmol/L at the bottom of the profile at 42.07m. Nitrate decreases in the surface waters from 39.66 μmol/L to 0 μmol/L. This large difference could be due to an anomaly or contamination as no other values reached this level.  It then increases in deeper waters from 0 to 0.23 μmol/L. Phosphate shows relatively constant behaviour down the water column increasing from 0.109 to 0.341 μmol/L.

Nitrate decreases in surface waters due to the biological uptake by organisms. Nitrate is used by organism to make nitrogenous bases used in the backbone of DNA. It then stay constant in deeper waters this could be due to the start of a bloom and the lack of dead material falling from the surface waters. Silicon is being completely stripped from surface waters this is due to the diatom bloom occurring assimilating the silicon for use in their silicious tests. Phosphate increases constantly even though it is assimilated by organisms; this is because nitrogen and silicon in the surface waters is limiting growth.

Nutrients- Figure 5

At 1.5m, the dissolved oxygen saturation is 90.4% and the chlorophyll is at a minimum with 2.8 µg/L. The graph shows corresponding dissolved oxygen and chlorophyll maximums at 20.5m of 97.6% and 4.61 µg/L. Chlorophyll decreases slightly to 4.6 µg/L at 42.1m, while oxygen saturation decreases to a minimum of 89.9%. The fluorometry profile does not agree with the chlorophyll concentrations from the Niskin bottle samples. The profile shows that the minimum should be at 42.1m, and this concentration is slightly lower than at 1.5m. This suggests a possible error in the chlorophyll sampling or processing.

The Secchi disk depth was 10m, which suggests a 1% light level at about 30m. Therefore, below this depth the oxygen saturation should be at a minimum because it is below the compensation depth, where respiration processes should dominate. This suggests a possible error in the dissolved oxygen sampling or processing.

Chlorophyll and  Dissolved Oxygen- Figure 4

A more gentle linear increase in fluorescence values occurs after 10 m, and this time reduced values are reached at 25 m. Temperature likewise does not display as rapid a reduction, occurring in two different stages before reaching its minimal value at 25 m.

The thermocline here seems to be even less distinct, which again means there is not as sharp a distinction as to where phytoplankton levels are at their highest. This trend could signify the movement from stratified waters to more mixed, coastal waters.

CTD- Figure 3

Backscatter: Vertical anomalies from CTD and nets, with a  clear region of high return from surface to 20m. From ensemble numbers 227412 to 227783 this seems to break up and fade out as R.V. Calista moved off station. Velocity and direction: There appears to be 3 distinct layers; the surface to 10m is moving slowly ( 0.1 to 0.2 m s-1) in a general SE direction, however this layer is likely distorted due to wave action. 10-20m is moving west at 0.3 m s-1,  20m to bottom is very slow moving (<0.1 m s-1). From 227412- 227788 this breaks down into a 2 layer system with a surface to 20m SE flow over a Northerly to Easterly flow. Both are slow at the boundary layer and increase in speed as you move away. On comparison with the underway data, this region appears to be a frontal system.

ADCP- Figures 1 & 2